1. Field of the Invention
The present invention relates to a golf club head. In particular, the present invention relates to a golf club head that is produced by means of joining two portions of the golf club head by friction welding.
2. Description of Related Art
A typical golf club head and a production method therefore are disclosed in, e.g., U.S. Pat. Nos. 5,769,307 and 5,885,170. As illustrated in FIGS. 1 and 2 of the drawings which respectively correspond to FIGS. 1 and 2 of U.S. Pat. Nos. 5,769,307 and 5,885,170, a typical golf club includes a head body 10, a hosel 20, and a shaft 30. The head body 10 is made of a metal material and includes a striking plate 11 on a front side thereof, with a heel 12 being formed on a side of the striking plate 11, and with an extension 13 extending upward from the heel 12 and having a flat abutting portion 131. Another flat abutting portion 22 is formed at a lower part of the hosel 20 that is formed of another metal material. The hosel 20 includes an engaging hole 21 in an upper part thereof for engaging with a lower end of a shaft 30.
A force F is applied to the head body 10 and the hosel 20 to make the flat abutting portion 131 abuts against the flat abutting portion 22. Then, the flat abutting portion 131 (or the flat abutting portion 22) is turned relative to the flat abutting portion 22 (or the flat abutting portion 131). With the friction heat, the head body 10 can be joined to the hosel 20.
Although the friction welding simplifies the manufacturing process and cuts the manufacturing cost in comparison to ordinary welding or brazing, several problems exist. Firstly, the metal material of the flat abutting portion 131 and the metal material of the flat abutting portion 22 melt and fuse with each other after friction welding, forming an intermetallic layer (not shown). Since the metal material (e.g., stainless steel) of the flat abutting portion 131 differs from that (e.g., titanium alloy) of the flat abutting portion 22 and thus provides poor compatibility in welding, the metallurgic structure of the intermetallic layer is detrimental to improvement of the bonding strength, resulting in a fragile structure or reducing the resilient deforming capability. As a result, the connection area between the head body 10 and the hosel 20 may break when proceeding with adjusting of inclination angle A of the hosel 20 of the golf club head product or when striking a golf ball. The good product ratio is reduced, and the life of the club head is shortened. Results of cannon shot tests showed that the head body 10 and the hosel 20 were apt to crack or break after being shot not more than 1000 times (a golf ball with a standard weight hits the striking plate 11 of the head body 10 at a velocity of 50 m/sec). The same problem exists when using friction welding to bond two portions of the club head that are made of different metals having insufficient compatibility.